Invention Help

[Binsky]

Hey everyone, I'm new to the site, and I need a little help. I'm working on a small invention that has proven to be a little more complicated than I thought. I wont go into too many details about what it is because I'm keeping it a secret until I can get a working prototype out.

What I'm basically making is a device that uses 2 nichrome heating coils that are 33mm in diameret, burning at 445C. My temperature readings aren't too accurate yet, because I'm stuck using the thermometer on my voltage meter until my IR one comes in. Depending on where I go with my design, the temperature of these coils may go down to about 290C.

I would like to install a devise kind of like what is in a hair dryer, because there will be air flowing through this thing, and I would like the coils to maintain a constant temperature. I have no idea what this devise would be called (other than a thermostat) or how to build one.

I also have no idea how to build the power supply for this thing, because so far using a 120V power supply salvaged from an old Iron has vaporized the nichrome wire I salvaged out of a toaster.

Any help anyone could provide would be awesome. I will update this with more details as soon as I figure them out.

 

[dknguyen]

If you want to use AC to power the nichrome wire use a triac and duty cycling if you need control finer than a relay. You can't use transistors since they only block current in one direction so they are DC only. Read up on triacs...they have a few quirks. THe main one being you can turn them on whenever you want, but you can't turn them off- they stay on until the current falls to zero, then they turn off (ie. when the AC signal crosses zero). As you can imagine, they can't be used for DC unless you want a one-time on switch.

If you use DC, you can just use a MOSFET and apply PWM signals to it to control the amount of power going into the nichrome. Really, the two are very similar, they are only different in the switch used and the quirks that come with the switch.

You can just buy a little AC-DC converter module to generate a low DC voltage in order to power your control electronics, but the power side of things is probably easiest just to use AC directly (after all, nichrome wire doesn't really care). Either way you have to build a switch that controls the power running through the nichrome so you can control the duty cycle.